| Reviewing the development of biochip, most of the first-generation biochip is based on optical measurement. However, there are some intrinsic defects in optical measurement, including complicated measuring process, limited accuracy, large measuring equipment and high costs, etc. In addition, it is impossible to make quantitative analysis with optical measurement. The second-generation biochip is based on magnetic measurement. It integrates all the functions of supporting equipment into the chip. The chip itself can process all the information, which moves the value of the system from the supporting system to the chip. Comparing with the first-generation biochip, the magnetic biochip has advantages in better cost-performance ratio, lower costs, higher accuracy and resolution, as well as better reliability. Furthermore, the chip is reusable, and it has the ability to quantitatively measure the number of biological molecules. Therefore, the magnetic biochip becomes very popular among researchers all over the world.The magnetic biochip mainly consists of three parts:magnetic measurement, identification of biological molecules, and circuit measurement. The main principle of magnetic measurement is to accomplish the magnetic measurement with the support of the giant magnetoresistance (GMR) effect generated from the spin valve film. Considering that most applications of the spin valve film are at room temperature, this paper focuses on studying the preparation conditions and performance optimizations of the spin valve film at room temperature.The first chapter introduces the concept and the development of biochip, and the operational principle of the first-generation biochip. The operating process of the second-generation biochip, the importance of this research to the second-generation biochip and the contents of this research together with its innovative points are emphasized in this chapter.Chapter2introduces the research object and content of spintronics, as well as the concept of giant magnetoresistance effect. It also introduces the structure and the operational principle of the spin valve which is fabricated based on the giant magnetoresistance effect and the process of the exchange bias effect in the ferromagnetic\antiferromagnetic bilayer in the spin valve. Applications of the spin valve in other fields are also introduced.Chapter3introduces the physical mechanism of spin transport. Several important physical concepts in optional spintronics are explained. A classical physical model, which is the physical model of magnetic resistance based on the Mott two fluid resistance, in optional spintronics is also introduced.Chapter4introduces the technology of magnetron sputtering, including its principle, technology and the equipment needed for film deposition. Meanwhile, annealing process of the spin valve film is demonstrated. At the end of this chapter, it describes the measuring equipment, methods and theory of magnetic resistance in detail.The main content of Chapter5is the whole layer optimization of the spin valve film, which improves the magnetoresistive value of spin valve, reduces the coercivity, and improves the work field. Firstly, this chapter introduces the structure of spin valve. Secondly, it respectively demonstrates how to improve the antiferromagnetic layer IrMn, the pinned layer CoFe, the isolation layer Cu, the free layer NiFe/CoFe and Ta buffer layer. Thirdly, the coercive force of spin valve is analyzed, and the characteristic of high frequency in spin valve film is also tested and analyzed.The last chapter summarizes the full paper. By applying the optimization method proposed by this paper, a spin valve with high magnetic resistivity, low coercivity and large exchange bias field is developed. The GMR of the demonstrated spin valve reaches6.5%, the free layer coercivity is2.4Oe, the exchange bias field is200Oe, and it has resonance peak under a high frequency of5.2GHz. Finally, a summary of current problems, future improvements, and subsequent work of this paper are presented. |
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